(a) Field of the Invention
The present invention concerns a process and apparatus for establishing a controlled atmosphere with a low content of oxygen in at least one first and one second compartments of a vessel for preserving fresh vegetables by means of a device for separating non-cryogenic air.
(b) Description of Prior Art
The long term storage of certain agricultural products, such as fruits, for example apples or kiwis, is currently ensured by means of refrigerated vessels. Certain recent devices additionally provide for maintaining controlled atmosphere with a low content of oxygen and carbon dioxide in this vessel, typically 2% for each of these components, said controlled atmosphere being obtained by separation from the air, by permeation or adsorption, and reduction of CO.sub.2 on activated carbon. This type of atmosphere, however, provides a good conservation of the aspect of the fruit only with the joint application of oxidizing products.
The Applicant has observed that a long term conservation without addition of anti-oxidizing products was possible with an atmosphere containing at most 1% oxygen and 1% carbon dioxide. Such an atmosphere cannot be kept at a reasonable cost through the present devices for air separation to provide a controlled atmosphere for conservation. On the other hand, this type of conservation presents particular seasonal specific aspects which do not justify the use of very costly devices for providing controlled atmospheres. As a matter of fact, in so far as apples are concerned, the user is typically provided with a certain number of compartments, for example 10, which may each contain 300 tons of apples. At the time of harvesting, the user loads the vessel of conservation at the rate of one compartment per day, in which the change from an ambient atmosphere to a controlled atmosphere of conservation should be obtained in less than 24 hours. Any loaded and conditioned compartment should thereafter be maintained for an extended period of time (which could exceed six months) under optimum conditions of conservation.